Leaving diagram inaccurate? (7,3)

I believe the answer is:

drawing out

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'leaving' is the definition.
The answer and definition can be both related to change as well as being present participle verbs.
Maybe there's a link between them I don't understand?

'diagram inaccurate?' is the wordplay.
'diagram' becomes 'drawing' (I am not sure about this - if you are sure you should believe this answer much more).
'inaccurate?' becomes 'out' (eg a calculation might be 'out').
'drawing'+'out'='DRAWING OUT'

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

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